(1) Field of the Invention
The present invention relates to a heavy duty pneumatic radial tire having an improved wear-resistant property, and more particularly to a heavy duty pneumatic radial tire adapted to prevent the extraordinary or irregular wear which often tends to occur at shoulders of the tires of this kind after continuously travel for long distances.
(2) Description of the Prior Art
In general, radial tires having at least two metal cord layers as a reinforcement for a belt are superior in wear-resistance and puncture-proof because between treads and carcass plies are arranged belts particularly tougher than in conventional bias tire. However, the radial tires are somewhat inferior in comfortability to ride due to the reinforcement by the belts. Accordingly, the radial tires which are also suitable for bad roads have been generally developed for good roads and have been recently widely used with the remarkable improvement of the road situation such as the extension and completion of super-highways.
On the other hand, however developed the roads or highways may be, they cannot completely avoid unevennesses such as seams of pavements or differences in level or partially unpaved roads. When radial tires of this kind are used for front wheels, they may be poor in stability of straight travelling owing to a tendency for a handle to be driven from the wheels running on the seams, stepped portions or tracks formed in the bad rods. Since this disadvantage results from the sufficient reinforcement of the entire tread by the belts, the round shoulders of tires wherein the shoulders are formed in a rounded-shape have been developed in order to avoid the disadvantage.
However, it has been found by experiments on such heavy duty radial tires having round shoulders that irregular wears having a depth and a width occur in the ends of contact surfaces of the treads which are apt to grow progressively toward the center of the tread and often cause the wear-resistance of the tire to be reduced. The irregular wear may be caused by the slip of shoulder portions due to the difference in rolling diameter thereof.